Member postings for chris boll 1

Regarding the crankshaft of the BollAero 1.8cc, my original had the prop driver screwed onto the shaft, this was the same as the ML Midge which inspired my engine design.

The small Sparey diesel also used this method. Ron Chernich drew the other alternative versions.

My aim was simplicity above all, the engine was originally published in Aviation Modeller magazine, which was not read by experienced model engineers, in general.

Ron also swapped sides of the exhaust and intake from my original, I prefer my original way for upright installation in a plane.

All my engine plans are now on the Outerzone website, with the magazine articles for the AMI 1.8 and 4.4cc.

The 7.5cc diesel is not included as I haven't got around to doing an assembly drawing, but three engines have been built from the component drawings and run well.

I have been very pleased that the 1.8cc has been made in many countries including Finland, Mexico and Argentina and all of these can be seen on YouTube

You have made many superb engines, I remember meeting you at Old Warden some years ago, when people used to run up vintage and self made model aero engines, sadly this seems to have lapsed recently.

I am approaching 80, but still follow my hobby of making and flying radio controlled planes, and this then led to making engines.

I am not a very good machinist, but as an ex engineer and designer I like to create simple engines that are easy to make. As others have said, overcoming the minor difficulties that arise helps to keep the brain working.

My original prototype really does have square fins to match the crankcase, but Keith's version does look superb, as usual. I did not find it a problem to cut them in the al alloy cylinder jacket. There are two to be seen running on YouTube, under BollAero 750.

For square pistons, the wind powered drainage mill that was rebuilt at the museum in Stowmarket does have them, and some modern pneumatic cylinders have been made with oval pistons, so the rod cannot rotate.

As always, Keith's workmanship and finish is far superior to my efforts, it gives me great pleasure to see what others make of my designs.

It proves that the engine is a good runner when made to the correct drawings, I much prefer working of a big sheet than thumbnail drawings scattered about.

As always, Keith's workmanship and finish is far superior to my efforts, it gives me great pleasure to see what others make of my designs.

It proves that the engine is a good runner when made to the correct drawings, I much prefer working of a big sheet than thumbnail drawings scattered about.

It sounds like it is too lean, l think problem is more likely to be in needle valve or fuel feed, fuel suction is normally good.

Check also if there is their an air leak into fuel line or air getting into crankcase.

It should still run even if cyl ports are not very accurate in liner.

Yes, the dimensions are correct, but I agree it is pictorially confusing.

ps Has anybody finished an engine and got it running yet?

A bit of clarification on the cylinder jacket top end. The 1.58 dia is the o.d. of the top part which projects .025 above the upper flange, the recess for the liner is 1.30 dia. See fig 7 on page 85. This is not very clear as shown.

On the subject of transfer ports, and all other machining operations on the 49 engine, I always use the most basic set ups , I do not own a rotary table, and try to assume many other builders will not have expensive equipment.

My previous engine articles were written for model aircraft magazines rather than ME, so the engines were first time projects for many people.

The exact width of transfer ports is not that critical, we are not trying to make a high performance racing engine. My ports were cut with a 3/16 cutter, and smoothed off with a file, the liner held in a vee block and repositioned by hand during milling, hence uneven edges before filing smooth. i .

I have now managed to sign into the forum, and I apologise for the drawing slips, Jason has already answered on my behalf to the queries so far.

I hope nobody has made too many scrap parts.....

I will keep an eye on future queries, and am also happy to be contacted direct on my e mail given at the end of part 3.